On June 27, 1997, the NEAR spacecraft, on its way to Eros, will make a
flyby (10 km/sec) of 253 Mathilde, a large C-asteroid 50 50
70 km across, with an extremely long rotation period (17.4
days, according to Mottola et al.). NEAR will approach Mathilde at a
phase angle of 139 and depart at 39 ; at closest approach
(1200 km) the phase will be near 80 . An imaging strategy has been
devised in which the spacecraft will obtain over 500 images in about 25
minutes around closest approach. The best resolution expected is 200
meters. Global imaging in seven colors between 0.4 and 1.1 m will
achieve a resolution of 500 meters. On departure a satellite search
will be made in which bodies as small as 100 meters across could be
detected. The flyby will determine the mass of Mathilde to better than
10%. The Mathilde flyby complements the Galileo flybys of Gaspra
and Ida by providing the first-ever closeup study of a C-type asteroid. The NEAR
flyby also represents the first time that such a study will be carried
out by a spacecraft with no scan platform.